1. Field of Invention
The present invention relates to a battery monitoring apparatus, and more particularly to a technique for accurately measuring residual capacity of a battery used in portable electronic devices.
2. Description of Related Art
Portable computers and other electronic devices are often powered by charge storage devices such as a battery. The battery is generally rechargeable and made of alkaline batteries in the form of an enclosure type nickel cadmium (Ni--Cd) battery or nickel metal hydride (Ni--MH) battery. Also, lithium ion (Li--ion) batteries of an organic electrolytic cell have been used in high-end portable electronic devices. The above rechargeable batteries require a charger for charging the batteries. The charger includes an internal charger equipped in the battery powered devices; this charger will begin charging the battery whenever the device is powered by AC power.
Further, the battery powered portable electronic devices often have the capability to monitor charge consumption from the battery so that the user can determine the remaining usage time before a required recharge or battery replacement. One prior battery monitoring system measured charge dissipation by measuring current drawn from the battery. In addition, some electronic devices and some battery monitoring system measured remaining battery capacity by checking the voltage across battery terminals. This monitoring system includes a microcontroller that reads the terminal voltage of a battery and calculates the remaining capacity corresponding to an input voltage level of the battery. The amount of battery capacity is converted into a battery gauge signal, preferably in a digital form, to be supplied with the host device such as a notebook computer. The host device displays the battery level via a display when it is requested by a user.
The operation of the above noted monitoring system is as follows. The microcontroller determines whether a battery gauge display key has been operated. The microcontroller detects the terminal voltage of the battery when the key has been operated. The terminal voltage input is compared to the battery level data stored in a memory, and the output is a battery gauge signal corresponding to the terminal voltage input. The stored battery level data corresponds to designated voltage intervals of a typical battery discharge curve. The voltage intervals are classified into several battery levels over time, and each battery level is designated by specific battery capacity data. The battery gauge signal is supplied with the host device to display the battery capacity data that is being denoted by percentage or bar graph via software.
However, the above noted monitoring system is inaccurate since it determines the remaining battery capacity based on the terminal voltage of the battery. It has been found that the battery residual capacity data is affected by battery temperature and battery self-discharge as well as operating conditions of the battery powered device; and much variation is revealed in the battery residual capacity data despite less variation in actual battery capacity.
Further, the battery gauge displaying scheme is inadequate for a user to get information on the remaining operating time of the battery. Thus, there is a need for a battery monitoring system that can provide the user with a prediction of the battery run time at various levels of power consumption.
Attempts have been made in the art of smart batteries to enable the reporting of accurate information to the host device for power management and charge control specific to the battery's state of charge and chemistry. The smart battery is equipped with specialized hardware that provides present state, and calculated and predicted information to its system host under software control. Details of such a smart battery are described in the Smart Battery Specifications jointly developed by Intel and Duracell, Inc. Those specifications define a system level solution for smart batteries, including the battery, the charger and the software layers.
Although this specification provides an ideal solution for many of issues related to batteries used in portable electronic devices, the smart battery device has a complicated construction and a high cost. Thus, the present invention is intended to provide the user with accurate residual battery capacity information along with an accurate prediction of the remaining operating time without using a smart battery.
The following patents each disclose features in common with the present invention but do not teach or suggest a technique for accurately determining the residual capacity of a dumb battery as in the present invention: U.S. Pat. No. 5,650,712 to Kawai et al., entitled Method For Detecting Remaining Battery Current, Voltage, And Temperature Capacity By Continuously Monitoring, U.S. Pat. No. 5,541,489 to Dunstan, entitled Smart Battery Power Availability Feature Based On Battery-Specific Characteristics, U.S. Pat. No. 5,600,230 to Dunstan, entitled Smart Battery Providing Programmable Remaining Capacity And Run-Time alarms Based On Battery-Specific Characteristics, U.S. Pat. No. 5,648,717 to Uskali, entitled Battery Charge Gauge With Current Integrator And Method For Gauging Battery Charge, U.S. Pat. No. 5,656,919 to Proctor et al., entitled Accurate Battery State-Of-Charge Monitoring And Indicating Apparatus And Method, U.S. Pat. No. 5,563,496 to McClure, entitled Battery Monitoring And Charging Control Unit, U.S. Pat. No. 5,652,502 to van Phuoc et al., entitled Battery Pack Having A Processor Controlled Battery Operating System, U.S. Pat. No. 5,444,378 to Rogers, entitled Battery State Of Charge Monitor, U.S. Pat. No. 5,191,291 to Taylor, entitled Method And Apparatus For Determining The Performance Capabilities Of Secondary Batteries, U.S. Pat. No. 5,659,240 to King, entitled Intelligent Battery Charger For Electric Drive System Batteries, U.S. Pat. No. 5,680,027 to Hiratsuka et al., entitled Battery Pack Including Internal Capacity Monitor For Monitoring Groups Of Battery Cells, U.S. Pat. No. 5,703,471 to Bullock et al., entitled Battery Protection Circuitry For Limiting Charging Parameters Of A Battery Plant, U.S. Pat. No. 5,606,243 to Sakai et al., entitled Battery State Judging Apparatus, U.S. Pat. No. 5,592,094 to Ichikawa, entitled Battery Discharge Characteristics Calculation Method And Remaining Battery Capacity Measuring Device, U.S. Pat. No. 5,561,362 to Kawamura et al., entitled Remaining Capacity Meter And Detection Method For Electric Vehicle Battery, U.S. Pat. No. 5,631,540 to Nguyen, entitled Method And Apparatus For Predicting The Remaining Capacity And Reserve Time Of A Battery On Discharge, U.S. Pat. No. 5,656,919 to Proctor et al., entitled Accurate Battery State-Of-Charge Monitoring And Indicating Apparatus And Method, U.S. Pat. No. 5,710,503 to Sideris et al., entitled On-Line Battery Monitoring System With Defective Cell Detection Capability, U.S. Pat. No. 5,412,307 to Yoshinatsu, entitled Residual Capacity Indicating Device, U.S. Pat. No. 5,012,176 to LaForge, entitled Apparatus And Method For Calorimetrically Determining Battery Charge State, U.S. Pat. No. 5,545,969 to Hasegawa, entitled Battery Residual Capacity Displaying System With Discharged Electrical Quantity Computation Section, U.S. Pat. No. 5,744,963 to Arai et al., entitled Battery Residual Capacity Measuring Apparatus And Method For Measuring Open-Circuit Voltages As The Battery Starts And Stops Supplying Power, U.S. Pat. No. 5,394,089 to Clegg, entitled Battery Monitor Which Indicates Remaining Capacity By Continuously Monitoring Instantaneous Power Consumption Relative To Expected Hyperbolic Discharge Rates, U.S. Pat. No. 5,422,822 to Toyota et al., entitled Apparatus For Detecting Remanent Stored Energy In Storage Battery And Apparatus For Warning Of Reduction In Remanent Stored Energy In Storage Battery, U.S. Pat. No. 5,518,835 to Simmonds, entitled Device For Indicating The Residual Capacity Of Secondary Cells, U.S. Pat. No. 5,614,829 to Song, entitled State-Of-Charge Measuring Method Using Multilevel Peukert's Equation, U.S. Pat. No. 5,617,324 to Arai, entitled Remaining Battery Capacity measuring Method And Apparatus, U.S. Pat. No. 5,650,712 to Kawai et al., entitled Method For Detecting Remaining Batterv Current, Voltage, And Temperature Capacity By Continuously Monitoring, U.S. Pat. No. 5,341,084 to Gotoh et al., entitled Method And Device For Determining And Indicating A Residual Capacity Of A Battery, U.S. Pat. No. 5,672,973 to Arai et al., entitled Apparatus For Monitoring Battery Residual Capacity In Multiple Modes, U.S. Pat. No. 5,789,923 to Shimoyama et al., entitled Battery Remaining Capacity Measuring Device, U.S. Pat. No. 5,809,449 to Harper, entitled Indicator Of Battery Current For Portable Devices, U.S. Pat. No. 5,699,050 to Kanazawa, entitled Battery Capacity Meter, U.S. Pat. No. 5,635,842 to Yokoo et al., entitled Method Of Estimating Residual Capacity Of Battery, and U.S. Pat. No. 5,680,027 to Hiratsuka et al., entitled Battery Pack Including Internal Capacity Monitor For Monitoring Groups Of Battery Cells.